Pro M tricks the computer as well... they use electronics to do so, C'n'L uses air flow thru a sample tube.
Either way you look at it, both meters trick the computer into seeing something that resembles stock parameters.
Pick your evil.
The only true way to have a proper functioning aftermarket MAM is to have a custom chip burned, then, no one is tricking the computer, the computer is recal'd based on the parameters at hand.
I ran the C'n'L with 19's, had great success (see sig.) and have since run the same C'n'L with new sample tube and 24's with no issues, running a very aggressive cam, and no custom chip for either setup.